Lecture 4 - The Periodic Table of Elements Tro, Chemistry:...

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Tro, Chemistry: A Molecular Approach 1 The Periodic Table of Elements
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Tro, Chemistry: A Molecular Approach 2 Elements with similar chemical and physical properties are in the same column Each period shows the pattern of properties repeated in the next period
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Tro, Chemistry: A Molecular Approach 3 = Alkali Metals = Alkali Earth Metals = Noble Gases = Halogens = Lanthanides = Actinides = Transition Metals
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Tro, Chemistry: A Molecular Approach 4 Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons Isotopes are atoms of the same element (X) with different numbers of neutrons in their nuclei X A Z H 1 1 H (D) 2 1 H (T) 3 1 U 235 92 U 238 92 Mass Number Atomic Number Element Symbol
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Example 2.3b How many protons, electrons, and neutrons are in an atom of ? for most stable isotopes, n 0 > p + Check: Z = 24 = # p + # e - = # p + = 24 Solution: in neutral atom, # p + = # e - mass number = # p + + # n 0 Concept Plan: Relationships: therefore A = 52, Z = 24 # p + , # e - , # n 0 Given: Find: Cr 52 24 Cr 52 24 symbol atomic number # p + # e - symbol numbers # n 0 A = Z + # n 0 52 = 24 + # n 0 28 = # n 0
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Tro, Chemistry: A Molecular Approach 6 Isotopes Soddy discovered that the same element could have atoms with different masses, which he called isotopes there are 2 isotopes of chlorine found in nature, one that has a mass of about 35 amu and another that weighs about 37 amu The observed mass is a weighted average of the weights of all the naturally occurring atoms the percentage of an element that is 1 isotope is called the isotope’s natural abundance the atomic mass of chlorine is 35.45 amu all isotopes of an element have the same number of protons, different numbers of neutrons
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Tro, Chemistry: A Molecular Approach 7 Neon 9.25%
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This note was uploaded on 05/20/2008 for the course CHEM 115 taught by Professor Larkin during the Spring '08 term at Bloomsburg.

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Lecture 4 - The Periodic Table of Elements Tro, Chemistry:...

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